Vehicle headlamp

Abstract

Vehicle headlamp provided with a metal halide lamp comprising a discharge vessel surrounded with clearance by an outer envelope and having a ceramic wall which encloses a discharge space containing xenon (Xe) and an ionizable filling, wherein in said discharge space two electrodes are arranged whose tips have a mutual interspacing EA so as to define a discharge path between them, wherein the discharge vessel has an internal diameter Di at least over the distance EA, and wherein Di is smaller than or equal to 2 mm and the relation EA/Di is smaller than 6, with the special feature that said vehicle headlamp has not more than one band-shaped light-absorbing coating laterally of the discharge path.

1 . Vehicle headlamp provided with a metal halide lamp comprising a discharge vessel surrounded with clearance by an outer envelope and having a ceramic wall which encloses a discharge space containing xenon (Xe) and an ionizable filling, wherein in said discharge space two electrodes are arranged whose tips have a mutual interspacing EA so as to define a discharge path between them, wherein the discharge vessel has an internal diameter Di at least over the distance EA, and wherein Di is smaller than or equal to 2 mm and the relation EA/Di is smaller than 6, characterized in that said vehicle headlamp has not more than one band-shaped light-absorbing coating laterally of the discharge path.  
     
     
         2 . Vehicle headlamp according to  claim 1 , wherein the band-shaped light-absorbing coating is provided on the outer side of the ceramic wall of the discharge vessel.  
     
     
         3 . Vehicle headlamp according to  claim 1 , wherein the band-shaped light-absorbing coating is provided on the inner side of the outer envelope.  
     
     
         4 . Vehicle headlamp according to  claim 1 , wherein the band-shaped light-absorbing coating is provided on the outer side of the outer envelope.  
     
     
         5 . Vehicle headlamp according to  claim 1 , wherein the band-shaped light-absorbing coating is located underneath a horizontal plane along a central axis of the metal halide lamp during operation, while an edge of the band-shaped light-absorbing coating directed towards said horizontal plane and the horizontal plane itself enclose an angle of substantially 15° with one another.  
     
     
         6 . Vehicle headlamp according to  claim 5 , wherein an edge of the band-shaped light-absorbing coating directed towards said horizontal plane and an edge of the band-shaped light-absorbing coating directed away from said horizontal plane enclose an angle of between 15° and 55° with one another.  
     
     
         7 . Vehicle headlamp according to  claim 1 , wherein the discharge vessel has a circumferential clearance inside the outer envelope of at most 5 mm.  
     
     
         8 . Vehicle headlamp according to  claim 1 , wherein the outer envelope is conically shaped and wherein the band-shaped light-absorbing coating—seen from a lamp cap supported by the outer envelope—extends in outward direction away from the discharge vessel.  
     
     
         9 . Vehicle headlamp according to  claim 1 , wherein the band-shaped light-absorbing coating has a profiled shape.  
     
     
         10 . Vehicle headlamp according to  claim 1 , wherein a central axis of the metal halide lamp is located at a distance above an optical axis of a reflector present in the headlamp during operation, said distance varying between 0.1 and 0.9 mm, being in particular 0.5 mm, more in particular 0.45 mm.  
     
     
         11 . A metal halide lamp to be used in a vehicle headlamp according to  claim 1.